The planetary systems addons for Celestia are largely obsolete for SE IMO, due to the texture maps. Procedural generation gives much higher detail with no file size attached. Celestia needed planet addons to have selection and diversity in its worlds, while SE does not. I have ported some of my own personal Celestia addons to SE though. Much of it can just be copied and pasted since many of the parameters are the same. The most incompatible thing would be atmospheres. It would be possible to write a program to convert one to the other, but all of the one's I've done have been converted by hand. The example of the direct conversion of one planet is below:

I wanted to make a full Star Trek addon by adding in many of the systems but the only maps I have are from Star Trek Online or from books and none give true distances.

I took a look at many of the systems in Celestia but even I know those distances can't be correct. Sadly all I have to go off of in terms of maps with names is the STO sector chart

Just not sure how I would translate this into planets and systems for SE. I already started making planets like Vulcan, Bajor, and a few others using their wiki images but I haven't placed most of them in any sort of correct area.

I wanted to make a full Star Trek addon by adding in many of the systems but the only maps I have are from Star Trek Online or from books and none give true distances.

They took a lot of liberty when creating the Star Trek universe and many of the locations and regions are either nonsensical or fanciful. You may have to use some artistic license... If doing ST systems in SE, it would almost certainly be better to start from scratch than try to convert Celestia documents, though those may certainly still make good references if no other good ones exist.

The STO sector chart is definitely not the most accurate possible map. I've seen much better maps for this type of project, but of course now that I'm looking for one I find nothing. You'll just have to hunt around, I know one exists.

Some worlds orbit known stars; Vulcan for example is generally accepted to orbit 40 Eri A. This would be a good place to start since the location is already known. The locations of other worlds can be estimated. For example, the travel time to Bajor from Earth is stated at least once in DS9; by making a best guess as to the warp factor involved you can limit the range of distances from Sol that Bajor could be at. Also, it is near Cardassian space, so if any Cardassian worlds have known locations this allows for a reasonable approximation of the location of Bajor. And so on.

EDIT: Come to think of it, I actually tried to place the Bajoran system in Celestia one time myself. These are the coordinates from that attempt:

For example, the travel time to Bajor from Earth is stated at least once in DS9; by making a best guess as to the warp factor involved you can limit the range of distances from Sol that Bajor could be at

Yeah I know about them mentioning it but they do not mention the warp factor. And I can tell you from lore that warp speed is a big factor in determining distance.

Yeah I know about them mentioning it but they do not mention the warp factor. And I can tell you from lore that warp speed is a big factor in determining distance.

I am very familiar with warp speeds. I know that none were mentioned, but they can often be inferred. For example, if there was a fleet traveling to assist DS9 against a Cardassian attack, then a speed of warp 8 is likely. Otherwise warp travel speeds are probably around 5 or 6. Not very precise, but good enough for ball park estimates.

Star Trek mod is on hold for now. I think I am going to wait for a future release of SE with multiple diffmaps supported and maybe ship lights. Also need to figure out what I am going to do now that my 3DS Max has expired.